I know that. If you're selling twelve seats at $10 dollars or sell six seats at $20, which way are you making more money? Answer: neither, it nets you not a penny more and you're still suffering the effects of overbuilding your stadium, either by having empty seats or low ticket prices to try to fill the overbuilt stadium.
That makes sense if that were the case, but all other things being equal, seat pricing has an elasticity lower than -1, so when you lower ticket prices, by a certain percentage, the volume of tickets sold increases by a higher percentage.
Of course, once you hit rock bottom on ticket price, and have strong fan survey results, and STILL have empty seats, it is at that point that you are really only building seats for a future promotion (or playoffs, as they draw larger crowds than regular season).